During dental care it is necessary to administer a local anesthesia to the patient. This injection is usually given in the gums and produces effects in the surrounding soft tissues. Aside from the discomfort that this represents for the patient, the efficacy of the anesthesia is not always optimal. This is essentially due to the fact that the anesthetic product partially diffuses away from the tooth being treated instead of remaining concentrated.
During dermatological treatment of man or animal, it is sometimes also useful to have a needle in order to perform a less painful or safer injection.
On certain needles, in order for the practitioner to work with precision, the base or connecting part of the needle, which may be made of plastic or metal and permits the needle to be screwed into the syringe, has a marking which indicates the positioning of the main bevel of the needle. Ordinarily the mark is on the side of the bevel, which means that when one views the needle from the side, one sees the mark and the main bevel at the same time.
However, this positioning of the mark does not permit the practitioner to use the bevel correctly, since the main bevel should be situated flatly on the mucosa or skin for a painless injection. The practitioner should therefore make certain that the needle is always turned in such a way that the mark is not visible, which does not correspond to accurate positioning but to a highly approximate positioning.
In order to alleviate the various problems described above, penetrating injection needles have been developed so as to make it possible, e.g., for the dentist to penetrate to the interior of the bone mass where the teeth are situated and deposit the anesthetic there. Therefore, the latter is deposited in the spongy interdental bone, resulting in immediate anesthesia of the teeth to be treated. The bone is surrounded by a cortical, i.e. a hard part forming a casing; the liquid anesthetic is less subject to the phenomenon of migration, which is not the case in a peripheral tissue irrigated by the blood. For the dermatologist and veterinarian the needles with a more cutting bevel permit the painless penetration of the surface layers of the skin.
The perforating injection needles were developed from the commonly used injection needles. Therefore, these perforating injection needles consist of a tubular body having two opposite ends, of which a first end provided with a single short bevel (posterior) is intended to be connected to means for driving in rotation and means for supplying or dispensing of the liquid. It is in reference to this bevel, during the fabrication, that the marking is positioned on the base, permitting the marking of the anterior bevel. The second end which is intended to penetrate into the human or animal body is provided with a long (anterior) bevel, constituting the main bevel which is supplemented by the other two bevels, the secondary bevels. According to the description, the main bevel specifies the face before the second end of the needle.
Now the second ends of the needles with their three bevels basically have one or another of two forms. According to the first form, which is the most widespread, the two secondary bevels are situated on the plane surface of the main bevel. They make the needle more pointed. This is the “lancet” bevel. According to the second form, less widespread than the first, the two secondary bevels are situated opposite the main bevel and therefore form counter-bevels. This arrangement of the three bevels gives the point of the needle a pyramid shape. This is the “back cut” bevel.
During use, in rotation, for a perforation by a needle having one or another of the arrangements of the triple bevel described above, the penetrating power into the bone mass is mediocre.
In addition, such injection needles have a point angle of the order of 60 degrees. The main bevel has an angle relative to the longitudinal axis of the needle of the order of 10 and 15 degrees.
However, in the course of various practical uses it has been found that these injection needles displace the tissues when an injection is made into the gingiva. The penetration is therefore quite painful. Moreover, these needles suffer from the fact that the angles formed by the intersection of the bevels between themselves or the bevels and the circular wall are close to or even greater than 60 degrees.